My invention is generally in the field of apparatus having a transducer such as a magnetic read/write head for reading and/or writing data on record media on which are formed a plurality or multiplicity of parallel tracks for the storage of such data. More specifically, my invention pertains to a mechanism in such data transfer apparatus for positioning the transducer with respect to the tracks on the record medium. The positioning mechanism of my invention is particularly well adaptable for use in apparatus for data transfer with a multitrack magnetic tape of cassette form, although I do not wish my invention to be limited to this particular application.
In the art of head positioning with respect to multitrack magnetic tape, it is not only a conventional, but rather a standard, design to employ an electric, bidirectional stepper motor in conjunction with a motion translating mechanism for transporting the head from track to track across the tape. Two U.S. patents are known to me that deal with the prior art. These are Yoshimaru U.S. Pat. No. 4,394,696 and Schoettle et al. U.S. Pat. No. 4,333,116. Both employ a lead screw as the motion translating mechanism.
Such head positioning mechanisms must transport the head across the tape between two predetermined limit positions on both sides of the parallel tracks. To stop the head exactly in at least one of these limit positions is of critical importance for subsequently transporting the head into precise alignment with the desired tracks. Either mechanical stops or optical sensors have usually been employed toward that end. Optical sensors with associated circuitry are rather expensive, and difficulties are involved in stopping the head in the exact positions required. Mechanical stops are less expensive and can more positively stop the head.
I have, however, found one serious weakness of the mechanical stops as heretofore constructed. The prior art stops have been fixedly disposed in the limit positions, with the head moving into direct abutment against them. Consequently, if the stepper motor remains in rotation after the head has come into abutment against either stop, as is required for subsequently initializing the head on a home track on the tape, then the full motor torque has been exerted on the motion translating mechanism. The threads of the lead screw and the part in engagement therewith have thus been susceptible to rapid abrasion, significantly shortening the useful life of the head positioning mechanism and, in consequence, of the entire data transfer apparatus.